Detecting the cold neutral gas in young radio galaxies James Allison Triggering Mechanisms for AGN
The First Large Absorption Survey in HI ASKAP FLASH will be one the first all-sky blind 21cm absorption surveys Sightlines to 15, radio sources 2hr Simulation 5 degrees 16, channels 4 km/s resolution FLASH: z =.5 1 WALLABY: z =.2 Image Credit: Matt Whiting and the ASKAPsoft Team 5 degrees 2
Detection Method Bayesian Model Comparison Our approach to the problem of detection is to ask a question: Given two model hypotheses about the system, which is warranted given the data? In our case Model 1 is a spectral-line & Model 2 is continuum-only In other words calculate the following ratio of conditional probabilities: Joint Posterior Marginal Likelihood or Bayes Evidence Prior 3
Detection Method Bayesian Model Comparison Marginal likelihood calculated by Monte-Carlo integration over parameters Implemented using Multi-Nest software Multiple line detections in a single spectrum Marginal Likelihood Parameter Likelihood Parameter Prior The statistic we want What we learn from the data ( Chi-squared ) What we knew before the observation (optical redshift etc ) 4
Method proven robust in simulations & real data 1 Simulations.5.5.1.15.2 z.7871.787 1.5 Real Data.7869.5.1.15.2.7869.787.7871 v (km s 1 ) 4 2 4 2 1.5 (Allison et al. 212a).5.1.15.2.7869.787.7871 z 1 2 3 4 5 v (km s 1 ) (Allison et al. 212b) 5
A Compact Array survey for absorption against compact radio sources We have conducted a 21cm absorption search targeting the most compact radio sources selected from ATCA 2GHz Survey Image Credit: Sarah Allison Morganti et al. (211) Search for cold HI gas by absorption in 45 host galaxies of young & compact radio galaxies Study kinematics of cold gas towards AGN -> Feeding & Feedback The Broadband Backend system on the Compact Array provides ASKAP-like test data for spectralline detection We simultaneously search for absorption in the redshift range z =.4.8 6
Detections from our Compact Sources samples The majority of detections are strong deep absorption lines ESO 473-G7 PKS B1814-637 (Allison et al. 212) 7
Detections from our Compact Sources sample Strong deep absorption lines are seen in edge-on disk like hosts ESO 473-G7 PKS 1814-63 1kpc (Allison et al. 212a) 8
Detection of a broad shallow line One tentative detection that looked different from our false detections PMN J254-4242 3 hours of integration time (Allison et al. 212) 9
Detection of a broad shallow line This was verified by longer integration time on the Compact Array PMN J254-4242 9 hours of integration time (Allison et al. 213) 1
Detection of a broad shallow line Broad shallow HI absorption redshifted towards the AGN (Allison et al. 213) 6dFGS Spectrum 1kpc Early-type Host galaxy 11
Why is this particular absorption-line interesting? Where is the deep narrow component? 5 km s -1 ESO 473-G7 PMNJ254-4242 12
Preparation for FLASH with existing all-sky data We have conducted a search for cold gas in radio galaxies in HIPASS Sample: Bright radio galaxies selected from the existing all-sky radio surveys; NVSS, SUMSS and MGPS-2; matched against optical redshifts in the HIPASS range S(1.4GHz) >~ 2mJy, Total: 21 galaxies (Allison et al. in prep.) Number of galaxies 18 Sample 1 16 14 12 1 8 6 4 2 32 28 24 2 16 12 8 4 2 4 6 8 1 12 cz sys (1 3 km s 1 ) Sample 2 13
4 detections in 21 nearby radio galaxies (z <.4) Associated absorption in HIPASS S (mjy) 5 5 1 2 2 4 4 8 MW v (km s 1 ) IRAS New 1359-247 absorption Cen A (NGC 5128) NGC 5793 5 5 Arp 22 (Allison et al. in prep.) 8 6 4 2 2 4 6 8 v (km s 1 ) 14
Thank You! Summary: The full ASKAP-FLASH will search for HI absorption towards more than 15, radio sources, enabling a study of the kinematics of cold gas surrounding AGN to redshifts higher than achievable by HI emission-line studies. We have tested our detection and modeling method in a search for HI absorption against compact young radio sources in the AT2G survey From existing results we expect to detect absorption lines in hundreds to thousands of radio galaxies up to z = 1, even with early ASKAP science (12+ antennas) However in order to interpret these detections we will need to follow up with high spatial resolution Image (VLBI) Credit: 21cm CASS observations and at o ther wavelengths (molecular and ionised gas ) 15